Russian Roulette, my mom and I got to be on the receiving end during one of my former step father's meth fueled rages, SCREW THAT.
Also, I am perfectly fine never having another facial laceration when I'm 60 miles from the nearest ambulance.
Things someone could probably convince me to do once:
Bungee jump, BASE jump, skydive, a ride in a fighter jet.

I think killing, but I don't know if I would be able to limit it to just one person I kill. I might enjoy killing and never stop, but Russian Roulette - I might try that once with the police just before execution day.